Transferring fluids between floating vessels on the open ocean in unprotected locations offers particular hazards in terms of personnel safety and damage to the vessels or facilities involved. The fluids which are transported in a transport vessel from a remote location may be delivered to either a tank located at an offshore facility, or by pipeline to a land-based receiving terminal. Offshore tank storage facilities may either be floating or settled on the seafloor.
No commercially proven technology exists that allows fluid transfer in harsh open ocean conditions between standard (non-dedicated) transport vessels or between such standard vessels and floating production and/or storage vessels. As an example, a floating storage vessel is a fixed asset near a market site that could be used for storing fluids for eventual delivery to on-shore facilities. For such floating storage vessels to become technically and commercially viable in many locations, a reliable fluid transfer system is needed that can transfer fluids between the storage vessel and standard transport carriers and other vessels having diverse features and configurations under a variety of conditions and with a sufficiently high berth availability.
Commercially proven technologies exist for oil transfer in harsh open ocean conditions, but such technologies require dedicated transport carriers with extensive bow modifications. Conversely, commercially proven technologies exist for oil transfer between a standard oil carrier and a floating storage vessel or a single point moored (SPM) buoy under benign sea conditions, however these conventional systems cannot operate in harsh open ocean conditions due to marine operations issues and safety concerns with support vessels, e.g. tugboats and offshore service vessels. No commercially proven system exists that can transfer fluids between a standard oil, gas or product carrier and a floating storage vessel in harsh open ocean conditions.
Conventionally, fluid transfer to and from floating transport vessels is most often accomplished thru articulated hard-pipe loading arms, such as, for example, an arm utilizing a Chiksan® swivel joint available from FMC Technologies, Inc., Houston, Tex. Fluid transfer operations using such loading arms generally require relatively benign conditions, such as those found in sheltered locations in harbors or behind breakwaters. As a result, many fluid transfer terminals currently in operation are located onshore, in harbors, bays, rivers or waters that are sheltered from open ocean conditions. Requiring protected fluid transfer sites limits the number of potential sites for new terminals, and in many regions a suitable site simply is not available. For example, on the U.S. west coast, few shallow water sites are available and meteorological and oceanographic (metocean) conditions (e.g., sea states, currents and winds) limit the number of potential solutions. Applying articulated loading arm technology in an open ocean location has been contemplated by some fluid transfer terminal projects. In shallow water locations with milder metocean conditions, a gravity based structure (GBS) which serves as a breakwater, thus allowing loading arms to be used in a side-by-side berthing layout, is a technically feasible solution. In deeper water applications, a floating storage vessel that is single point moored allows the vessel to weathervane into the dominant metocean conditions, thus minimizing floating storage vessel motions. Loading arms have been proposed for fluid transfer between two vessels in a side-by-side berthing (mooring) arrangement, but have not been employed to date for a variety of reasons. Unlike a GBS, a floating storage vessel does not serve as a breakwater, and thus side-by-side moorings must take the full force of the metocean conditions. Predicting the relative motions between the vessels with the necessary high degree of certainty has thus far proven to be difficult. Optimizing the mooring line arrangement in a side-by-side mooring is difficult in that the vessels are often very close in overall length, and thus proper bow and stern mooring line geometries cannot be achieved. Also, tugboat operational problems are further compounded by the approach layout in a side-by-side berthing. Additional concerns include damage to the vessels due to high relative motions between the vessels, and increased potential for breakout due to high loads on the mooring lines. All these issues combine to produce significant concerns for conventional fluid transfer systems in side-by-side offshore berthing concepts, and thus the ability to meet fluid delivery commitments.
Development work to date on new offshore fluid transfer systems has primarily concentrated on vessels that are moored in a tandem arrangement. This applies to the transfer of cryogenic fluids, where the development work has primarily concentrated on aerial systems and more recently on floating hose systems. It has been found that these systems can require the use of dedicated transport carriers which use complicated and expensive technology which often is not widely endorsed by the maritime industry and which can be difficult to operate in other than benign weather conditions. None of these systems have solved the problem of how to safely deliver and connect the fluid transfer hose, pipe or conduit between vessels in harsh open ocean conditions. Other ‘in-water’ bottom founded systems have been conceptualized, as well as a variety of platform based concepts, all of which utilize either loading arms or aerial hoses, but have yet to resolve the problems stated above.
There has been renewed interest in the industry in floating hose based transfer systems, particularly for cryogenic fluids. The appeal of a floating hose based system is that it mimics tandem ship-to-ship oil transfer systems, which are well understood, and have a proven history of safe, successful operation in relatively benign environments. However, there are several significant concerns for any floating hose system for cryogenic fluid transfer. Hose manufacturers have only recently begun work to explore ways to retrieve and deploy the hose between liftings, and there are technical difficulties with the existing concepts. In particular, the means of lifting the hoses out of the water and connecting them to the floating transport vessel manifold and supporting them during the transfer operation is problematic and has yet to be defined. Moreover, how to manage the hoses during an emergency disconnect is likewise unresolved.
For floating hose based oil transfer systems, a system capable of operating in harsh open ocean environments and of connecting to a standard carrier's midship manifold would significantly improve operability and safety while elevating terminal berth availability.
It would be desirable to have a fluid transfer system that provides safe operation, high berth availability, universal applicability, regardless of ship design and features, and convenient conduit handling methods for offshore fluid transfer between floating vessels. It would further be desirable for the fluid transfer system to be supported by the hull structure and not supported by the manifold flanges. It would further be desirable to have a fluid transfer system in which a fluid flow conduit is attached to a standard manifold flange on the transport vessels without exceeding the allowable design loads, i.e. axial force and shear. It would further be desirable to have a fluid transfer system that could accommodate standard floating transport vessels with few modifications.